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        <h2 id="如何渲染几万条数据并不卡住界面"><a href="#如何渲染几万条数据并不卡住界面" class="headerlink" title="如何渲染几万条数据并不卡住界面"></a>如何渲染几万条数据并不卡住界面</h2><p><a href="https://developer.mozilla.org/zh-CN/docs/Web/API/Window/requestAnimationFrame" target="_blank" rel="noopener">MDN文档</a></p>
<pre><code>&lt;script&gt;
    setTimeout(() =&gt; {
      // 插入十万条数据
      const total = 100000;
      // 一次插入 20 条，如果觉得性能不好就减少
      const once = 20;
      // 渲染数据总共需要几次
      const loopCount = total / once;
      let countOfRender = 0;
      let ul = document.querySelector(&quot;ul&quot;);
      function add() {
        // 优化性能，插入不会造成回流
        const fragment = document.createDocumentFragment();
        for (let i = 0; i &lt; once; i++) {
          const li = document.createElement(&quot;li&quot;);
          li.innerText = Math.floor(Math.random() * total);
          fragment.appendChild(li);
        }
        ul.appendChild(fragment);
        countOfRender += 1;
        loop();
      }
      function loop() {
        if (countOfRender &lt; loopCount) {
          window.requestAnimationFrame(add);
        }
      }
      loop();
    }, 0);
  &lt;/script&gt;
</code></pre><a id="more"></a>
<h2 id="监控"><a href="#监控" class="headerlink" title="监控"></a>监控</h2><p>对于代码运行错误，通常的办法是使用 <code>window.onerror</code> 拦截报错。该方法能拦截到大部分的详细报错信息，但是也有例外</p>
<ul>
<li>对于跨域的代码运行错误会显示 <code>Script error.</code> 对于这种情况我们需要给 <code>script</code> 标签添加 <code>crossorigin</code> 属性</li>
<li>对于某些浏览器可能不会显示调用栈信息，这种情况可以通过 <code>arguments.callee.caller</code> 来做栈递归</li>
</ul>
<p>对于异步代码来说，可以使用 <code>catch</code> 的方式捕获错误。比如 <code>Promise</code> 可以直接使用 <code>catch</code> 函数，<code>async await</code> 可以使用 <code>try catch</code></p>
<p>但是要注意线上运行的代码都是压缩过的，需要在打包时生成 sourceMap 文件便于 debug。</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line">window.onerror = function(msg, url, line, col, error) &#123;</span><br><span class="line">  // 直接将错误打印到控制台</span><br><span class="line">  alert(JSON.stringify(arguments));</span><br><span class="line"></span><br><span class="line">  // 方便在未打开控制台的时候，记录错误对象</span><br><span class="line">  window.demoError = arguments;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>对于捕获的错误需要上传给服务器，通常可以通过 <code>img</code> 标签的 <code>src</code> 发起一个请求。</p>
<h2 id="存储"><a href="#存储" class="headerlink" title="存储"></a>存储</h2><p>cookie，localStorage，sessionStorage，indexDB</p>
<table>
<thead>
<tr>
<th>特性</th>
<th>cookie</th>
<th style="text-align:right">localStorage</th>
<th style="text-align:right">sessionStorage</th>
<th style="text-align:right">indexDB</th>
</tr>
</thead>
<tbody>
<tr>
<td>数据生命周期</td>
<td>一般由服务器生成，可以设置过期时间</td>
<td style="text-align:right">除非被清理，否则一直存在</td>
<td style="text-align:right">页面关闭就清理</td>
<td style="text-align:right">除非被清理，否则一直存在</td>
</tr>
<tr>
<td>数据存储大小</td>
<td>4K</td>
<td style="text-align:right">5M</td>
<td style="text-align:right">5M</td>
<td style="text-align:right">无限</td>
</tr>
<tr>
<td>与服务端通信</td>
<td>每次都会携带在 header 中，对于请求性能影响</td>
<td style="text-align:right">不参与</td>
<td style="text-align:right">不参与</td>
<td style="text-align:right">不参与</td>
</tr>
</tbody>
</table>
<p>从上表可以看到，<code>cookie</code> 已经不建议用于存储。如果没有大量数据存储需求的话，可以使用 <code>localStorage</code> 和 <code>sessionStorage</code> 。对于不怎么改变的数据尽量使用 <code>localStorage</code> 存储，否则可以用 <code>sessionStorage</code> 存储.</p>
<p>对于 <code>cookie</code>，我们还需要注意安全性。</p>
<table>
<thead>
<tr>
<th>属性</th>
<th>作用</th>
</tr>
</thead>
<tbody>
<tr>
<td>value</td>
<td>如果用于保存用户登录态，应该将该值加密，不能使用明文的用户标识</td>
</tr>
<tr>
<td>http-only</td>
<td>不能通过 JS 访问 Cookie，减少 XSS 攻击</td>
</tr>
<tr>
<td>secure</td>
<td>只能在协议为 HTTPS 的请求中携带</td>
</tr>
<tr>
<td>same-site</td>
<td>规定浏览器不能在跨域请求中携带 Cookie，减少 CSRF 攻击</td>
</tr>
</tbody>
</table>
<h2 id="框架通识"><a href="#框架通识" class="headerlink" title="框架通识"></a>框架通识</h2><ol>
<li><h3 id="MVVM-由以下三个内容组成"><a href="#MVVM-由以下三个内容组成" class="headerlink" title="MVVM 由以下三个内容组成"></a>MVVM 由以下三个内容组成</h3><ul>
<li>View：界面</li>
<li>Model：数据模型</li>
<li>ViewModel：作为桥梁负责沟通 View 和 Model</li>
</ul>
<p>在 JQuery 时期，如果需要刷新 UI 时，需要先取到对应的 DOM 再更新 UI，这样数据和业务的逻辑就和页面有强耦合</p>
<p>在 MVVM 中，<strong>UI 是通过数据驱动的</strong>，数据一旦改变就会相应的刷新对应的 UI，UI 如果改变，也会改变对应的数据。这种方式就可以在业务处理中只关心数据的流转，而无需直接和页面打交道。<strong>ViewModel 只关心数据和业务的处理，不关心 View 如何处理数据</strong>，在这种情况下，View 和 Model 都可以独立出来，任何一方改变了也不一定需要改变另一方，并且可以将一些可复用的逻辑放在一个 ViewModel 中，让多个 View 复用这个 ViewModel。</p>
<p>在 MVVM 中，最核心的也就是数据双向绑定，例如 Angluar 的脏数据检测，Vue 中的数据劫持。</p>
</li>
<li><h3 id="Angular脏数据检测"><a href="#Angular脏数据检测" class="headerlink" title="Angular脏数据检测"></a>Angular脏数据检测</h3><p>当触发了指定事件后会进入脏数据检测，这时会调用 <code>$digest</code> 循环遍历所有的数据观察者，判断当前值是否和先前的值有区别，如果检测到变化的话，会调用 <code>$watch</code> 函数，然后再次调用 <code>$digest</code> 循环直到发现没有变化。循环至少为二次 ，至多为十次。</p>
<p>脏数据检测虽然存在低效的问题，但是不关心数据是通过什么方式改变的，都可以完成任务，但是这在 Vue 中的双向绑定是存在问题的。并且脏数据检测可以实现批量检测出更新的值，再去统一更新 UI，大大减少了操作 DOM 的次数。所以低效也是相对的，这就仁者见仁智者见智了。</p>
</li>
<li><h3 id="Vue数据劫持"><a href="#Vue数据劫持" class="headerlink" title="Vue数据劫持"></a>Vue数据劫持</h3><p>Vue 内部使用了 <code>Obeject.defineProperty()</code> 来实现双向绑定，通过这个函数可以监听到 <code>set</code> 和 <code>get</code>的事件。</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br></pre></td><td class="code"><pre><span class="line">var data = &#123; name: &apos;test&apos; &#125;</span><br><span class="line">observe(data)</span><br><span class="line">let name = data.name // -&gt; get value</span><br><span class="line">data.name = &apos;yyy&apos; // -&gt; change value</span><br><span class="line"></span><br><span class="line">function observe(obj) &#123;</span><br><span class="line">  // 判断类型</span><br><span class="line">  if (!obj || typeof obj !== &apos;object&apos;) &#123;</span><br><span class="line">    return</span><br><span class="line">  &#125;</span><br><span class="line">  Object.keys(data).forEach(key =&gt; &#123;</span><br><span class="line">    defineReactive(data, key, data[key])</span><br><span class="line">  &#125;)</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line">function defineReactive(obj, key, val) &#123;</span><br><span class="line">  // 递归子属性</span><br><span class="line">  observe(val)</span><br><span class="line">  Object.defineProperty(obj, key, &#123;</span><br><span class="line">    enumerable: true,</span><br><span class="line">    configurable: true,</span><br><span class="line">    get: function reactiveGetter() &#123;</span><br><span class="line">      console.log(&apos;get value&apos;)</span><br><span class="line">      return val</span><br><span class="line">    &#125;,</span><br><span class="line">    set: function reactiveSetter(newVal) &#123;</span><br><span class="line">      console.log(&apos;change value&apos;)</span><br><span class="line">      val = newVal</span><br><span class="line">    &#125;</span><br><span class="line">  &#125;)</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>以上代码简单的实现了如何监听数据的 <code>set</code> 和 <code>get</code> 的事件，但是仅仅如此是不够的，还需要在适当的时候给属性添加发布订阅</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">&lt;div&gt;</span><br><span class="line">    &#123;&#123;name&#125;&#125;</span><br><span class="line">&lt;/div&gt;</span><br></pre></td></tr></table></figure>
<p>在解析如上模板代码时，遇到 <code></code> 就会给属性 <code>name</code> 添加发布订阅。</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br></pre></td><td class="code"><pre><span class="line">// 通过 Dep 解耦</span><br><span class="line">class Dep &#123;</span><br><span class="line">  constructor() &#123;</span><br><span class="line">    this.subs = []</span><br><span class="line">  &#125;</span><br><span class="line">  addSub(sub) &#123;</span><br><span class="line">    // sub 是 Watcher 实例</span><br><span class="line">    this.subs.push(sub)</span><br><span class="line">  &#125;</span><br><span class="line">  notify() &#123;</span><br><span class="line">    this.subs.forEach(sub =&gt; &#123;</span><br><span class="line">      sub.update()</span><br><span class="line">    &#125;)</span><br><span class="line">  &#125;</span><br><span class="line">&#125;</span><br><span class="line">// 全局属性，通过该属性配置 Watcher</span><br><span class="line">Dep.target = null</span><br><span class="line"></span><br><span class="line">function update(value) &#123;</span><br><span class="line">  document.querySelector(&apos;div&apos;).innerText = value</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line">class Watcher &#123;</span><br><span class="line">  constructor(obj, key, cb) &#123;</span><br><span class="line">    // 将 Dep.target 指向自己</span><br><span class="line">    // 然后触发属性的 getter 添加监听</span><br><span class="line">    // 最后将 Dep.target 置空</span><br><span class="line">    Dep.target = this</span><br><span class="line">    this.cb = cb</span><br><span class="line">    this.obj = obj</span><br><span class="line">    this.key = key</span><br><span class="line">    this.value = obj[key]</span><br><span class="line">    Dep.target = null</span><br><span class="line">  &#125;</span><br><span class="line">  update() &#123;</span><br><span class="line">    // 获得新值</span><br><span class="line">    this.value = this.obj[this.key]</span><br><span class="line">    // 调用 update 方法更新 Dom</span><br><span class="line">    this.cb(this.value)</span><br><span class="line">  &#125;</span><br><span class="line">&#125;</span><br><span class="line">var data = &#123; name: &apos;yck&apos; &#125;</span><br><span class="line">observe(data)</span><br><span class="line">// 模拟解析到 `&#123;&#123;name&#125;&#125;` 触发的操作</span><br><span class="line">new Watcher(data, &apos;name&apos;, update)</span><br><span class="line">// update Dom innerText</span><br><span class="line">data.name = &apos;yyy&apos;</span><br></pre></td></tr></table></figure>
<p>接下来,对 <code>defineReactive</code> 函数进行改造</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br></pre></td><td class="code"><pre><span class="line">function defineReactive(obj, key, val) &#123;</span><br><span class="line">  // 递归子属性</span><br><span class="line">  observe(val)</span><br><span class="line">  let dp = new Dep()</span><br><span class="line">  Object.defineProperty(obj, key, &#123;</span><br><span class="line">    enumerable: true,</span><br><span class="line">    configurable: true,</span><br><span class="line">    get: function reactiveGetter() &#123;</span><br><span class="line">      console.log(&apos;get value&apos;)</span><br><span class="line">      // 将 Watcher 添加到订阅</span><br><span class="line">      if (Dep.target) &#123;</span><br><span class="line">        dp.addSub(Dep.target)</span><br><span class="line">      &#125;</span><br><span class="line">      return val</span><br><span class="line">    &#125;,</span><br><span class="line">    set: function reactiveSetter(newVal) &#123;</span><br><span class="line">      console.log(&apos;change value&apos;)</span><br><span class="line">      val = newVal</span><br><span class="line">      // 执行 watcher 的 update 方法</span><br><span class="line">      dp.notify()</span><br><span class="line">    &#125;</span><br><span class="line">  &#125;)</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
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                      start = 0;
                    }
                    if (end < position + word.length) {
                      end = position + word.length;
                    }
                    if(end > content.length){
                      end = content.length;
                    }
                    slicesOfContent.push(mergeIntoSlice(content, start, end, indexOfContent));
                  }

                  // sort slices in content by search text's count and hits' count

                  slicesOfContent.sort(function (sliceLeft, sliceRight) {
                    if (sliceLeft.searchTextCount !== sliceRight.searchTextCount) {
                      return sliceRight.searchTextCount - sliceLeft.searchTextCount;
                    } else if (sliceLeft.hits.length !== sliceRight.hits.length) {
                      return sliceRight.hits.length - sliceLeft.hits.length;
                    } else {
                      return sliceLeft.start - sliceRight.start;
                    }
                  });

                  // select top N slices in content

                  var upperBound = parseInt('1');
                  if (upperBound >= 0) {
                    slicesOfContent = slicesOfContent.slice(0, upperBound);
                  }

                  // highlight title and content

                  function highlightKeyword(text, slice) {
                    var result = '';
                    var prevEnd = slice.start;
                    slice.hits.forEach(function (hit) {
                      result += text.substring(prevEnd, hit.position);
                      var end = hit.position + hit.length;
                      result += '<b class="search-keyword">' + text.substring(hit.position, end) + '</b>';
                      prevEnd = end;
                    });
                    result += text.substring(prevEnd, slice.end);
                    return result;
                  }

                  var resultItem = '';

                  if (slicesOfTitle.length != 0) {
                    resultItem += "<li><a href='" + articleUrl + "' class='search-result-title'>" + highlightKeyword(title, slicesOfTitle[0]) + "</a>";
                  } else {
                    resultItem += "<li><a href='" + articleUrl + "' class='search-result-title'>" + title + "</a>";
                  }

                  slicesOfContent.forEach(function (slice) {
                    resultItem += "<a href='" + articleUrl + "'>" +
                      "<p class=\"search-result\">" + highlightKeyword(content, slice) +
                      "...</p>" + "</a>";
                  });

                  resultItem += "</li>";
                  resultItems.push({
                    item: resultItem,
                    searchTextCount: searchTextCount,
                    hitCount: hitCount,
                    id: resultItems.length
                  });
                }
              })
            };
            if (keywords.length === 1 && keywords[0] === "") {
              resultContent.innerHTML = '<div id="no-result"><i class="fa fa-search fa-5x" /></div>'
            } else if (resultItems.length === 0) {
              resultContent.innerHTML = '<div id="no-result"><i class="fa fa-frown-o fa-5x" /></div>'
            } else {
              resultItems.sort(function (resultLeft, resultRight) {
                if (resultLeft.searchTextCount !== resultRight.searchTextCount) {
                  return resultRight.searchTextCount - resultLeft.searchTextCount;
                } else if (resultLeft.hitCount !== resultRight.hitCount) {
                  return resultRight.hitCount - resultLeft.hitCount;
                } else {
                  return resultRight.id - resultLeft.id;
                }
              });
              var searchResultList = '<ul class=\"search-result-list\">';
              resultItems.forEach(function (result) {
                searchResultList += result.item;
              })
              searchResultList += "</ul>";
              resultContent.innerHTML = searchResultList;
            }
          }

          if ('auto' === 'auto') {
            input.addEventListener('input', inputEventFunction);
          } else {
            $('.search-icon').click(inputEventFunction);
            input.addEventListener('keypress', function (event) {
              if (event.keyCode === 13) {
                inputEventFunction();
              }
            });
          }

          // remove loading animation
          $(".local-search-pop-overlay").remove();
          $('body').css('overflow', '');

          proceedsearch();
        }
      });
    }

    // handle and trigger popup window;
    $('.popup-trigger').click(function(e) {
      e.stopPropagation();
      if (isfetched === false) {
        searchFunc(path, 'local-search-input', 'local-search-result');
      } else {
        proceedsearch();
      };
    });

    $('.popup-btn-close').click(onPopupClose);
    $('.popup').click(function(e){
      e.stopPropagation();
    });
    $(document).on('keyup', function (event) {
      var shouldDismissSearchPopup = event.which === 27 &&
        $('.search-popup').is(':visible');
      if (shouldDismissSearchPopup) {
        onPopupClose();
      }
    });
  </script>





  

  
  <script src="https://cdn1.lncld.net/static/js/av-core-mini-0.6.4.js"></script>
  <script>AV.initialize("bVaMPlLlY6iLfKTJxt2dwg2W-gzGzoHsz", "wUyT08JP6LOCTUtp6jMn0oIY");</script>
  <script>
    function showTime(Counter) {
      var query = new AV.Query(Counter);
      var entries = [];
      var $visitors = $(".leancloud_visitors");

      $visitors.each(function () {
        entries.push( $(this).attr("id").trim() );
      });

      query.containedIn('url', entries);
      query.find()
        .done(function (results) {
          var COUNT_CONTAINER_REF = '.leancloud-visitors-count';

          if (results.length === 0) {
            $visitors.find(COUNT_CONTAINER_REF).text(0);
            return;
          }

          for (var i = 0; i < results.length; i++) {
            var item = results[i];
            var url = item.get('url');
            var time = item.get('time');
            var element = document.getElementById(url);

            $(element).find(COUNT_CONTAINER_REF).text(time);
          }
          for(var i = 0; i < entries.length; i++) {
            var url = entries[i];
            var element = document.getElementById(url);
            var countSpan = $(element).find(COUNT_CONTAINER_REF);
            if( countSpan.text() == '') {
              countSpan.text(0);
            }
          }
        })
        .fail(function (object, error) {
          console.log("Error: " + error.code + " " + error.message);
        });
    }

    function addCount(Counter) {
      var $visitors = $(".leancloud_visitors");
      var url = $visitors.attr('id').trim();
      var title = $visitors.attr('data-flag-title').trim();
      var query = new AV.Query(Counter);

      query.equalTo("url", url);
      query.find({
        success: function(results) {
          if (results.length > 0) {
            var counter = results[0];
            counter.fetchWhenSave(true);
            counter.increment("time");
            counter.save(null, {
              success: function(counter) {
                var $element = $(document.getElementById(url));
                $element.find('.leancloud-visitors-count').text(counter.get('time'));
              },
              error: function(counter, error) {
                console.log('Failed to save Visitor num, with error message: ' + error.message);
              }
            });
          } else {
            var newcounter = new Counter();
            /* Set ACL */
            var acl = new AV.ACL();
            acl.setPublicReadAccess(true);
            acl.setPublicWriteAccess(true);
            newcounter.setACL(acl);
            /* End Set ACL */
            newcounter.set("title", title);
            newcounter.set("url", url);
            newcounter.set("time", 1);
            newcounter.save(null, {
              success: function(newcounter) {
                var $element = $(document.getElementById(url));
                $element.find('.leancloud-visitors-count').text(newcounter.get('time'));
              },
              error: function(newcounter, error) {
                console.log('Failed to create');
              }
            });
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        },
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          console.log('Error:' + error.code + " " + error.message);
        }
      });
    }

    $(function() {
      var Counter = AV.Object.extend("Counter");
      if ($('.leancloud_visitors').length == 1) {
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      } else if ($('.post-title-link').length > 1) {
        showTime(Counter);
      }
    });
  </script>



  

  

  

  

  

</body>
</html>
